1. Field of the Invention
The present invention relates to a polypropylene resin composition useful as an adhesive, and more particularly, to a polypropylene resin composition useful as an adhesive for bonding a polypropylene resin layer and an ethylene/vinyl alcohol copolymer layer or a nylon layer.
2. Description of the Related Art
Laminates comprising a polypropylene resin layer and an ethylene/vinyl alcohol copolymer layer, or a polypropylene resin layer and a nylon layer, are low in oxygen permeability and moisture vapor permeability and are widely used for containers for foods and medicines.
However, since adhesion between a polypropylene resin layer and an ethylene/vinyl alcohol copolymer layer or a nylon layer is poor, a molding method is generally employed wherein a bonding layer is placed between the resin layers by co-extrusion to laminate the layers.
It is well known that polyolefin resins graft-modified with an unsaturated carboxylic acid or derivatives thereof may be used as a bonding layer (see for example Japanese patent application Laid-Open Nos. 5527/1973, 98784/1976, and 26548/1977). It is also known that the bonding strength between the resin layers may be improved by adding a low-density polyethylene to the graft-modified polyolefin resin (see for example Japanese Patent Publication No. 40113/1979), adding a high-density polyethylene to the graft-modified polyolefin resin (see for example Japanese Patent Publication No. 36586/1984), or adding a hydrocarbon elastomer to the graft-modified polyolefin resin (see for example Japanese Patent Publication No. 40112/1979).
When compositions prepared by adding a low-density polyethylene, an ethylene polymer, or a hydrocarbon elastomer to a graft-modified polyolefin resin are employed as an adhesive layer, their performance is inadequate. For example, when a laminate made up of a polypropylene resin layer and an ethylene/vinyl alcohol copolymer layer or a nylon layer is blow molded into a bottle, the thin section of the product is low in adhesion strength. Therefore, further improvement is sought.